1. Field of the Invention
The present invention relates generally to branch pipe lining techniques, and more particularly, to a pipe lining method which is suitable for lining a branch pipe as well as a main pipe.
2. Description of the Related Art
When an underground pipe, such as pipelines and passageways, becomes defective or too old to perform properly, the pipe is repaired and rehabilitated without digging the earth to expose the pipe and disassembling the sections of the pipe. This non-digging method of repairing an underground pipe has been known and practiced commonly in the field of civil engineering. The pipe lining method utilizes a tubular pipe liner bag made of a resin absorbent material impregnated with a hardenable resin, and having the outer surface covered with a highly air-tight plastic film. The tubular pipe liner bag is inserted into a pipe to be repaired by means of a pressurized fluid such that the pipe liner bag is turned inside out as it proceeds deeper in the pipe. Hereinafter, this manner of insertion shall be called "everting". When the entire length of the tubular liner bag is everted (i.e., turned inside out) into the pipe, the everted tubular liner is pressed against the inner wall of the pipe by a pressurized fluid, and the tubular flexible liner is hardened as the hardenable resin impregnated in the liner is heated, which is effected by heating the fluid filling the tubular liner bag. It is thus possible to line the inner wall of the defective or old pipe with a rigid liner without digging the ground and disassembling the pipe sections.
The foregoing pipe lining method can be similarly applied to the lining of a main pipe of sewerage pipes or the like and a branch pipe or a plurality of branch pipes branched off the main pipe. More specifically, the lining of a branch pipe employs a branch pipe liner bag which typically comprises a tubular resin absorbent material having a hardened flange at one end and the outer surface coated with a highly air-tight plastic film, and an unhardened hardenable resin impregnated in the tubular resin absorbent material. This branch pipe liner bag is introduced into a main pipe. With the flange of the branch pipe liner bag closely connected to the circumference of a branch pipe opening of a main pipe, the branch pipe liner bag is everted (i.e. turned inside out) into the branch pipe from the main pipe toward the ground surface by a pressurized fluid, and pressed onto the inner wall of the branch pipe. Then, while the branch pipe liner bag is being kept pressed onto the inner wall, the branch pipe liner bag is heated or otherwise processed to cause a hardenable resin impregnated therein to harden, thus completing the lining of the branch pipe.
With the conventional branch pipe liner bag, however, the flange is formed such that its inner diameter becomes identical to the inner diameter of the hardened tubular resin absorbent material. It is therefore difficult to exactly position the cylinder of the flange, supported by a working robot introduced into the main pipe, to the branch pipe opening and fit the flange into the branch pipe from the branch pipe opening while monitoring the inside of the main pipe with a TV camera. This work requires expertise and a lot of time.
If inexact positioning of the flange of the branch pipe liner bag to the branch pipe opening causes a slight shift of the flange from the branch pipe opening, the shifted portion of the branch pipe liner bag is wrinkled.
To eliminate this problem, the inventors of the present invention have previously proposed an improved branch pipe liner bag in Japanese Patent Application No. 9-176166, as illustrated in FIG. 6. Specifically, the illustrated branch pipe liner bag 1 has a flange 3 whose inner diameter dl is smaller than the inner diameter d of a hardened tubular resin absorbent material 2.
However, when the branch pipe liner bag 1 according to the above-mentioned proposal is used to line a branch pipe 11 as illustrated in FIG. 6, a clearance space S1 is formed between a cylinder portion 3b continuous to the flange 3 of the hardened branch pipe liner bag 1 and the branch pipe 11, causing the following problems.
Specifically, if a load due to ground subsidence, earthquake or the like acts on a main pipe 10 buried in the ground, a load stress concentrates on the connection of the main pipe 10 and the branch pipe 11. Since the cylinder portion 3b continuous to the flange 3 of the branch pipe liner bag 1 is not in close contact with the opening of the branch pipe 11 or the inner wall of the branch pipe 11 due to the clearance space S1, it cannot be protected by surrounding walls from deformations due to an external load. Thus, the cylinder portion 3b exhibits a lower resistance to a load than other portion of the branch pipe liner bag which is hardened in close contact with the inner wall of the branch pipe 11.